A. Field of Invention.
This invention pertains generally to the adjustment of a video image on a cathode ray tube and more particularly to alignment of a video image on a cathode ray tube in various magnetic fields.
B. Definitions.
Align means to cause a video image to be adjusted so that distortion characteristics are reduced and the video image that is displayed on the cathode ray tube forms an image that is pleasing to the eye.
Calibrated magnetic field strength signal means the signal or data representative of the actual magnetic field as measured by a calibrated magnetometer.
Calibration magnetometer means a magnetometer used to measure magnetic field strength and direction and generate calibrated magnetic field strength signals representative of the actual magnetic field.
Cathode ray tube means a device that is capable of displaying an image that uses a magnetically deflected electron beam. A cathode ray tube may include one or more of the following: the tube structure, the phosphor screen, the neck of the tube, the deflection and control windings, including the yoke, rotation and other coils, and the electron guns.
Characterization module means a device that is normally coupled in some manner to a cathode ray tube and may include a storage device for storing correction factor data and/or magnetic correction factor data. The characterization module can also store term multipliers, gain matrix tables, magnetic gain matrix tables, magnetic correction data formulas, or other data for use in aligning displays including cathode ray tube monitors.
Correction factor data means the encoded digital bytes or any other form of data or signals, such as term multipliers that are used to modify standardized transformation equations, that are representative of the amount of correction required to adjust the correction factor parameters to substantially align a video image on a cathode ray tube.
Correction factor parameters means the various geometry characteristics of the cathode ray tube including horizontal size, raster rotation, vertical size, horizontal center, vertical center, pincushioning, vertical linearity, keystoning, convergence, etc., and various electron gun characteristics of the cathode ray tube including contrast, brightness, luminosity, focus, color balance, color temperature, electron gun cutoff, etc., as well as other adjustments to a cathode ray tube.
Correction signals means any signals generated by monitor circuitry that can be used in the process of aligning a video image on a cathode ray tube.
CRT magnetometer means a magnetometer associated with a cathode ray tube that senses the magnetic field data surrounding the cathode ray tube and generates noncalibrated magnetic field strength signals.
Decoder means a device for interpreting encoded correction factor data and locale specific correction factor data and generating a signal or data in response. Decoders may include PWMs, PDMs, DACs, interpolation engines, screen display chips, or other similar devices.
Driver signals are the electrical signals that are used to drive the deflection and control windings and electron guns of a cathode ray tube.
Dynamically adjusting means to alter or change correction factor parameters during the course of a scan.
Induced magnetic field means the magnetic field generated by a magnetic field generator.
Local magnetic field means the magnetic field surrounding a cathode ray tube device that does not include the induced magnetic field produced by a magnetic field generator.
Locale specific correction factor data means data or signals representative of the amount of correction required to align a video signal on a cathode ray tube in a magnetic field. The locale specific correction factor data may be in the form of term multipliers that are used to modify standardized transformation equations as disclosed in U.S. Pat. No. 5,216,504 issued Jun. 1, 1993, entitled "Automatic Precision Video Monitor Alignment System", or as a magnetic gain matrix table or a magnetic correction data formula which can be used to modify correction factor data obtained by screen mapping using a vision system as disclosed in U.S. patent application Ser. No. 08/638,222 filed Apr. 26, 1996, entitled "Screen Mapping of a Cathode Ray Tube", or other devices.
Logic device means a microprocessor, a state machine, a digital signal processor or other logic devices.
Magnetic correction data means the data or signals that can be used to alter correction factor data to generate locale specific correction factor data. Magnetic correction data is representative of the amount of correction required for various correction factor parameters in various magnetic fields.
Magnetic correction data formula means a mathematical representation of the variation of various correction factor parameters as a function of the variation in the local magnetic field.
Magnetic distortion means the amount of distortion of a substantially aligned image due to a magnetic field.
Magnetic field means a local magnetic field and/or an induced magnetic field.
Magnetic field generator means a device for altering and/or controlling the magnetic field surrounding a cathode ray tube.
Magnetic field state means the magnitude of the three-dimensional components of the magnetic field surrounding a cathode ray tube.
Magnetic field strength signals means the signals or data representative of the three-dimensional components of a magnetic field and may take the form of a calibrated and/or noncalibrated magnetic field strength signal.
Magnetic gain matrix table means a table used to indicate how correction factor data, for each correction factor parameter, can be altered to compensate for changes in a magnetic field to maintain alignment of a video image display. The table may comprise noncalibrated magnetic field strength signals and associated magnetic correction data.
Memory comprises any desired storage medium including, but not limited to, EEPROMs, RAM, EPROMs, PROMs, ROMs, magnetic storage, magnetic floppies, bar codes, serial EEPROMs, flash memory, etc.
Monitor circuitry means one or more circuits that generate correction signals, including driver signals to align a cathode ray tube in response to locale specific correction factor data. Monitor circuitry is not necessarily located in the cathode ray tube monitor but can be located external thereto, or in any other device.
Noncalibrated magnetic field strength signal means the signal or data representative of a magnetic field measured by a noncalibrated or production grade magnetometer.
Nonvolatile storage device means a memory device that is capable of storing data that does not require a constant supply of power.
Processor means a logic device including, but not limited to, state machines, microprocessors, digital signal processors, etc.
Term multipliers means factors generated by measuring distortion characteristics of a cathode ray tube for use with transformation equations to produce a correction signal.
Transformation equation means a standard form equation for producing a correction voltage waveform to correct common distortion characteristics of a cathode ray tube.
Video image means the displayed image that appears on a cathode ray tube screen.
Vision system means a system for measuring distortion characteristics and producing correction factor data and magnetic correction data that is used for aligning or adjusting video images on a cathode ray tube. The use of a vision system is described, for example, in U.S. Pat. No. 5,216,504.
C. Description of the Background.
Recent developments in the measurement of distortion and the adjustment of video images on cathode ray tube devices, including computer monitors and digital television displays, have made it possible and desirable to correct video displays for various types of distortion. Magnetically induced distortion has not previously been corrected for local magnetic variations. For example, the effect of earth's magnetic field on a video image varies significantly with both geographic location and the orientation of the cathode ray tube relative to the earth magnetic field. Although attempts have been made through monitor design to minimize magnetically induced distortion effects, these efforts are at best a compromise and usually provide less than desirable results. Correcting magnetic distortion is an important factor in providing overall distortion correction, since most correction factor parameters vary with the magnetic operating environment of the monitor.
Heretofore, cathode ray tube devices were calibrated at the factory for the general geographic location in which they were expected to be used. For example, a manufacturer might have separate calibration standards for North America, Europe, Australia, etc. This method is inherently limited, because the same calibration is applied over a wide geographic area and does not address field orientation or local magnetic variations. However, magnetic distortion often varies significantly with the orientation of the cathode ray tube and with the local magnetic field. For example, it is not uncommon for the alignment of a monitor to change significantly by simply rotating the monitor through 90 degrees or using the monitor in a different area of the country. Since prior art devices have been unable to correct for local magnetic distortion, it would therefore be desirable to provide a system and method to accurately maintain the alignment of a cathode ray tube video display in a wide range of magnetic field operating environments.